7/20=21/60＜25/60=5/12,∴7/20＜5/12
3/4=15/20＞8/20=2/5,∴3/4＞2/5
4/5=32/40＞25/40=5/8,∴4/5＞5/8
3/16=9/48＜28/48=7/12,∴3/16＜7/12